DE69511263T2 - MANUFACTURING A THERMOELECTRIC POWER GENERATION UNIT - Google Patents

Description

TECHNICAL AREA

The present invention relates to a method of manufacturing a thermoelectric power generating unit, which is manufactured by electrically connecting a series of a plurality of thermocouples as thermoelectric power generating elements, each of which is manufactured by connecting dissimilar semiconductors to each other.

BACKGROUND TECHNOLOGY

A thermocouple develops a voltage when different temperatures are applied to opposite ends of it. Thermoelectric power generation uses the voltage as electrical energy.

Thermal power generation has recently attracted much attention as an effective means of converting thermal energy directly into electrical energy including the use of waste heat. In particular, a thermoelectric power generation unit used to generate thermoelectric power has attracted much attention because of its possibility of application to micro-sized portable electronic equipment, such as a wristwatch, since it has thermocouples connected in series, and further it does not cause a problem of battery depletion or leakage of the electrolyte in a battery as is the case with a redox battery.

Fig. 46 is a perspective view showing an example of a structure of a conventional thermoelectric power generation unit. This thermoelectric power generation unit The power generation unit has a laminated structure as a whole, and comprises a plurality of thermocouples 100 made of P-type thermoelectric material 101 and N-type thermoelectric material 102; a large number of thermocouples serving as thermoelectric power generation elements are provided in a predetermined manner and electrically connected in series.

A hot junction 104 and a cold junction 105 of corresponding thermocouples 100 are provided on the upper surface and the lower surface of the thermoelectric power generation unit with the laminated structure so that power is generated by a temperature difference between the two surfaces.

Thermoelectric power is generated by using the so-called "Seebeck effect" where two dissimilar metals are joined at opposite ends and a temperature difference is maintained between the two junctions, a thermoelectric electromotive force is generated between the two junctions.

Such a thermoelectric power generation unit for generating a thermoelectric power as described above is normally manufactured by the following method.

First, powdered alloy particles are sintered to form an ingot of a processing material; thermal P- and N-type semiconductor materials in ingot form are prepared by what is called the "sintering process".

Then each block formed from corresponding thermoelectric materials is cut and broken into chips in the shape of a rectangular parallelepiped by a dice saw or similar. The chips with the rectangular parallelepiped epiped shape are arranged in a matrix manner as shown in Fig. 46, in which a P-type thermoelectric material 101 and an N-type thermoelectric material 102 are alternately provided.

Subsequently, a thermoelectric power generation unit having a plurality of thermocouples connected in series is manufactured by connecting the opposite ends (at the hot junction 104 and the cold junction 105, respectively) of adjacent chips to a conductive member such as a metal plate or the like, such connections being formed mainly by soldering.

Typically, the conventional thermoelectric power generation unit manufactured by the above-mentioned method is of a shape of several tens of cm2 or larger and has dozens of thermocouples.

The output of a conventional thermocouple composed of a Bi-Te-based material, which is believed to have the highest performance among all the thermoelectric materials in practical use, is on the order of 400 uV/ºC per thermocouple.

A wristwatch, which is portable electronic equipment, is normally used in an environment at about room temperature, and thus a large temperature difference between any parts inside a wristwatch cannot be expected; the size of the material is required to generate a voltage required to drive a wristwatch, namely 1.5 V or more.

This may not be a problem if a thermoelectric power generation unit can be increased in size. However, it is very hard to integrate as many as 2000 thermocouples in a space of 1 cm², which is essentially equivalent to the size of a button-sized cell. The size of the thermoelectric power generation unit is particularly important when it is to be used as a power source for a wristwatch and other micro-sized electronic equipment.

Simply put, the miniaturization of thermoelectric power generation units can only be achieved if a sintered body of thermoelectric materials can be cut into very small pieces by mechanical processing as stated in the foregoing.

Machining of micro-sized devices obviously has its limitations, and due to the very fragile nature of most thermoelectric materials, care must be taken not only during the cutting process but also in handling them after cutting, which inevitably results in lower production yields.

The minimum size of a material that can be handled by the conventional method of manufacturing by machining is considered to be about 1 mm², and even if a thermoelectric power generation unit is packed into a space of 1 cm², the maximum number of thermoelectric power generation elements, namely thermocouples, incorporated therein is estimated to be only about 50 elements.

There is another conceivable method of manufacturing a thermoelectric power generation unit in which a thermoelectric material is formed in a thin film form by the vacuum deposition process, small-sized thermocouples are manufactured by forming the micro-sized thermoelectric material in a thin film form by the etching process, and the thus-manufactured thermocouples are connected in series, thereby forming a thermoelectric power generation unit. generation unit is completely terminated. Of course, the production of small-sized thermocouples is easier with this process.

The film formed by the vacuum deposition process is about 1 µm in thickness, which is too thin for assembling thermocouples for use as thermoelectric power generating elements, and when as many as 2000 such thermocouples are in place, their internal impedance becomes too high, causing a risk that the thermocouples are unable to output a current required by the thermoelectric power generating elements. Therefore, thermocouples made of films formed by the vacuum deposition process are unsuitable for use as the thermoelectric power generating elements.

Another process that has been proposed for forming the thermoelectric power generating elements is the so-called thick film process, in which a Bi-Te-based alloy is deposited in a paste state and then sintered to form a film that is significantly thicker than the film formed by the vacuum deposition process.

The method of manufacturing a thermoelectric power generating element by the thick film process is disclosed, for example, in Japanese Patent Application Laid-Open No. JP 563-70462A.

By the thick film process disclosed in JP S63-70462A, fine patterning by screen printing is possible, and further, a film having a thickness of 10 µm can be formed. For this reason, the thick film process is more suitable for forming thermoelectric power generation elements with a low internal impedance than the method of forming a thin film by the vacuum deposition process.

However, the thick film process is very complicated because it requires several pre-processing steps including: melting of initial process materials such as Bi, Te, Sb, Se or similar, making an alloy blank from mixed molten metals and crushing the blank to make the powdered alloy paste without allowing the process materials to simply be mixed and applied in their raw state.

Furthermore, this process presents risks in that the process materials are contaminated by impurities in one of the pre-processing steps for producing the pasty material, that an uneven distribution of the chemical composition occurs in the material as shown above due to the failure of a uniform solid solution, and that cracks occur in the course of sintering.

With this process, patterning by screen printing is possible, but high-precision manufacturing of the micro-sized thermoelectric power generation elements is difficult to achieve. For the reasons given in the foregoing, the thick-film process is not good enough to provide thermoelectric power generation elements with sufficient properties, and therefore it is not the most suitable method for manufacturing micro-sized thermoelectric generation devices.

As is clear from the foregoing description, it is difficult to manufacture a thermoelectric power generation unit by integrating a number of thermocouples as the thermoelectric power generation elements in a very small area by means of either the conventional mechanical processing method or the manufacturing method by etching the film formed by the conventional vacuum deposition process. and a manufacturing process for a micro-sized thermoelectric power generation unit with a sufficient output capacity is available so far.

On the other hand, as stated above, the thick film process is not completely satisfactory in view of the complex nature of the process and the product properties.

From JP 63-84171A a method of manufacturing a thermoelectric sensor of arbitrary shape is known, in which a lower metal electrode formed on an insulating substrate by electroless plating and electric plating is formed, an n-type metal layer formed on the lower electrode by electric plating is formed, a p-type metal layer not in contact with the n-type metal layer is formed, and an upper metal layer in contact with the upper surfaces of both metal layers is provided. By such a structure of the electrodes that the lower and upper electrodes are formed at the end portion in the direction of the thickness of the plating film, namely an n-type metal layer and a p-type metal layer.

It is an object of the present invention to provide a manufacturing method of high accuracy and with ease a micro-sized thermoelectric power generation unit having a sufficient output capacity as a generator as well as a high-accuracy patterning capability, while solving the problems encountered by the conventional manufacturing methods of a thermoelectric power generation unit.

This object is achieved by a manufacturing method of a thermoelectric power generation unit comprising the steps as given in claim 1.

Preferred embodiments of the invention are specified in the subclaims.

Referring to claim 7, it is desirable that the width of each of the openings in the first pattern in the form of stripes is wider than that of each of the unopened surface areas therein, and that the second pattern in the form of stripes is identical to the first pattern in the form of stripes.

Also, in the respective manufacturing methods of a thermoelectric power generation unit according to the invention as described in the foregoing, the use of a photosensitive dry film made of acrylic resin or a photosensitive polyimide resin is recommended for a photosensitive resin with which a pattern in the form of stripes is formed on a substrate or an electrode film formed thereon.

In the above-mentioned manufacturing methods of a thermoelectric power generation unit, patterning with a photosensitive resin is provided, and thermoelectric bodies are formed by a plating process within openings of the photosensitive resin. Consequently, a thermoelectric power generation element (thermocouples) having a thickness of several tens of µm can be formed with high accuracy.

Further, since the thermoelectric bodies are formed by the plating process, the thermoelectric bodies can be formed with a thickness in the range of 10 µm to about 100 µm, and the chemical composition of the thermoelectric bodies can be easily controlled by adjusting the chemical composition of the plating bath and an applied voltage.

The manufacturing process of a thermoelectric power generation unit according to the invention includes the lithographic process using a photosensitive resin, the plating process, the vacuum deposition process, and the etching process. Therefore, a plurality of elements can be formed simultaneously on a batch basis, thereby enabling the integration density of the thermocouples, namely, the thermoelectric power generation elements, to jump dramatically from the conventional level. As a result, a micro-sized thermoelectric power generation unit that generates a high output even at a small temperature difference can be manufactured with ease.

In the method of forming a thermoelectric power generating element, respective thermoelectric assemblies comprise thermoelectric bodies formed by plating in openings of a photosensitive resin having a pattern in the form of stripes. Consequently, slippage, if any, in the cross-sectional position of the thermoelectric bodies is minimized by stacking a plurality of thermoelectric assemblies containing thermoelectric bodies made of different thermoelectric materials so that the unopened surface areas of the photosensitive resin on one thermoelectric assembly smoothly fit into the openings (plated portion) of the photosensitive resin on one.

As a result, the distance between dissimilar thermoelectric materials automatically falls within a predetermined range, making pattern matching easier when thermoelectric structures are bonded together; when wiring between thermoelectric bodies is provided by a vacuum deposition process or photolithographic techniques, the work can be carried out with ease by preparing a mask corresponding to the predetermined distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 to 8 illustrate a first embodiment carrying out the manufacturing method of a thermoelectric power generation unit according to the invention. Also, Fig. 1 to 3 and Fig. 7 illustrate a second and third embodiment, Fig. 4 and 5 illustrate the second embodiment as above, Fig. 8 illustrates the second, fourth and fifth embodiments according to the invention.

Fig. 9 illustrates a part of the manufacturing process adopted in the second embodiment which carries out the manufacturing method of a thermoelectric power generation unit according to the invention.

Figs. 10 to 13 illustrate the manufacturing process adopted in the third embodiment according to the invention. Also, Figs. 11 and 12 illustrate a sixth embodiment. Fig. 13 illustrates the sixth and ninth embodiments.

Figs. 14 to 18 illustrate the manufacturing process adopted in the fourth embodiment according to the invention. Also, Figs. 14 and 15 illustrate the fifth and sixth embodiments, Figs. 17 and 18 illustrate the fifth embodiment.

Fig. 19 illustrates a part of the manufacturing process adopted in the fifth embodiment according to the invention.

Fig. 20 illustrates a part of the manufacturing process adopted in the sixth embodiment according to the invention.

Fig. 21 to 28 illustrate the manufacturing process adopted in a seventh embodiment according to the invention. Also, Fig. 21 to 23 illustrate the eighth to twelfth embodiments, Fig. 25 illustrates a tenth embodiment, Fig. 26 to 28 illustrate the eighth embodiment.

Fig. 29 illustrates a part of the manufacturing process adopted in the eighth and eleventh embodiments according to the invention.

Figs. 30 to 32 illustrate the manufacturing process adopted in the ninth embodiment according to the invention. Also, Fig. 30 illustrates the twelfth embodiment.

Figs. 33 and 34 illustrate a part of the manufacturing process adopted in the tenth and eleventh embodiments according to the invention.

Figs. 35 and 36 illustrate a part of the manufacturing process adopted in the twelfth embodiment according to the invention.

Figs. 37 to 35 illustrate the manufacturing process adopted in a thirteenth embodiment according to the invention.

Fig. 46 is a perspective view showing a shape of a thermoelectric power generation unit manufactured by the conventional method.

BEST MODE FOR CARRYING OUT THE INVENTION

The manufacturing method of a thermoelectric power generation unit according to the invention will be described in detail by the following description of examples of preferred embodiments with reference to the accompanying drawings.

[First embodiment]

Referring to Figs. 1 to 8, the manufacturing method of a thermoelectric power generation unit according to the invention by the first embodiment will be described hereinafter.

Referring now to Fig. 1, a substrate 10 is formed from a copper sheet, and an electrode film 11 is deposited on the substrate 10 by a vacuum deposition process using titanium (Ti). The electrode film 11 has a thickness of 500 nm.

A titanium film of the electrode film can protect a copper sheet of the substrate 10 from being attacked by a plating solution during a plating treatment, which will be described hereinafter.

Subsequently, a photosensitive resin film is formed on the electrode film 11. The photosensitive film 12 is formed by a roll coater using a photosensitive dry film of 50 µm in thickness.

Then, as shown in Fig. 1, a pattern in the form of stripes is provided in the photosensitive resin 12 by means of a lithographic technique consisting of a light exposure treatment for impinging objects with light through a photomask and a development treatment for dissolving and removing only unexposed portions. Fig. 7 is a plan view showing the shape of the pattern provided in the photosensitive resin 12.

After the photosensitive resin 12 is formed, a Teflon-based polymer film is formed on the entire surface of the bottom surface of the substrate by a spin coating process (not shown in Fig. 1).

The polymer film made of a Teflon-based material formed on the bottom surface of the substrate 10 is effective for preventing a metallic deposit from being formed on the substrate 10 during the plating process described below.

In the next step, first thermoelectric bodies 15 made of a first thermoelectric material are formed by a plating process in openings 13 provided in the photosensitive resin 12 on the substrate 10, as shown in Fig. 2.

A Bi-Te-Se alloy, which is an N-type semiconductor, is used as the material for the first thermoelectric bodies 15.

A plating electrolyte used to form the first thermoelectric bodies 15 is a nitric acid solution containing Bi(NO3)3, TeO2 and SeO2. The Bi-Te-Se alloy is deposited on the electrode film 11 within the openings 13 of the photosensitive resin 12 by applying 1 V between the electrode film 11 serving as a cathode and a platinum (Pd) electrode serving as an anode.

By plating as above, the first thermoelectric bodies 15 are formed on the electrode film 11 only in the areas inside the openings 13 surrounded by the photosensitive resin 12, since the bottom surface of the substrate 11 is protected by the polymer film.

In the plating process for forming the first thermoelectric bodies 15, the amount of metal deposition is determined according to the amount of electric charge, which can be calculated based on the electric current consumed during electrolysis. For this reason, the thickness of the first thermoelectric bodies 15 can be easily controlled within a desired range by measuring the amount of electric charge.

The amount of the reaction electric charge is set so that the first thermoelectric bodies 15 have the same thickness as the photosensitive resin 12 in which the pattern is provided, as shown in Fig. 2, namely 50 µm.

Further, the chemical composition of the alloy can be changed by varying the ion concentration of Bi, Te and Se contained in the plating electrolyte, and the selection of the material for the first thermoelectric bodies 15 having a required output voltage and resistance value becomes possible by varying the set conditions for the ion concentration of the above-mentioned metals.

After the plating of the first thermoelectric bodies 15 is completed, the polymer film is peeled off and removed from the bottom surface of the substrate 10 using toluene, and then the thermoelectric bodies 15 formed on the substrate 10 are heat-treated in a nitrogen atmosphere at 350°C for one hour.

The heat treatment in a nitrogen atmosphere is used to homogenize the composition of the alloy constituting the first thermoelectric bodies 15 so that the output of the thermoelectric power generating elements is enhanced.

Then, as shown in Fig. 3, the entire surface of the substrate 10 is coated with a thermosetting resin 16 consisting of a polyimide resin by a spin coating process.

Thereafter, a heat treatment at a temperature of 150ºC or higher is applied to cure the thermosetting resin 16 consisting of polyimide resin.

Subsequently, after dissolving all the copper constituting the substrate (10) by immersing the whole body thereof in a nitric acid solution, the titanium (Ti) constituting the electrode film is dissolved using a 1% hydrofluoric acid solution.

In this dissolution treatment process, the first thermoelectric bodies 15, the photosensitive resin 12 and the thermosetting resin 16 remain as they are as shown in Fig. 4 since they are all insoluble in nitric acid and hydrofluoric acid, thereby forming a first thermoelectric assembly 20.

The foregoing describes the process of forming the first thermoelectric assembly 20 including the first thermoelectric bodies 15, and a second thermoelectric assembly 21 as shown in Fig. 5 is formed by the same process as described in the foregoing, except for a process of forming second thermoelectric bodies 17 by plating with a second thermoelectric material. The process of forming the second thermoelectric bodies 17 by plating with the second thermoelectric material will be described hereinafter.

After the process shown in Fig. 1 is completed, the second thermoelectric bodies 17 made of the second thermoelectric material are formed in the openings 13 provided in a thermoelectric resin 12 by means of a plating process (not shown).

A Bi-Te-Sb alloy, which is a P-type semiconductor, is used as the material for the second thermoelectric bodies 17.

A plating electrolyte used to form the second thermoelectric bodies 17 of the P-type semiconductor is a nitric acid solution containing Bi(NO₃)₃, TeO₂ and SbCl₃.

The Bi-Te-Sb alloy is deposited on an electrode film 11 within the openings 13 provided in the photosensitive resin 12 by applying 1 V between the electrode film 11 serving as a cathode and a platinum (Pt) electrode serving as an anode.

In this plating process, the second thermoelectric bodies 17 are also deposited only within the openings 13 provided in the photosensitive resin 12, since the bottom surface of a substrate 10 is protected by a polymer film formed thereon; the thickness of each of the second thermoelectric bodies 17 can be controlled by measuring the amount of the reaction electric charge so that each has the same thickness as that of a dry film, namely, 50 µm.

The composition of the alloy constituting the second thermoelectric bodies 17 can also be changed by varying the ion concentration of Bi, Te and Sb contained in the plating electrolytes, the composition of the thermoelectric bodies 17 can be controlled to have the desired output voltage and resistance.

The second thermoelectric structure 21 can be formed, as shown in Fig. 5, by applying the same treatment processes as those used to manufacture the first thermoelectric structure 20 described above with reference to Figs. 1 to 4 and 7, namely, the dissolving treatment of the polymer film formed on the bottom surface of the substrate, the heat treatment, the coating process of the substrate 10 with the thermosetting resin 16, and the process of dissolving the substrate 10 and the electrode film 11.

In the next step, alternate layers of the first thermoelectric assembly 20 and the second thermoelectric assembly 21 are formed, bonded together by an epoxy-based adhesive, and cut into a predetermined length, thereby forming a laminated thermoelectric assembly having a sectional view as shown in Fig. 6.

If the surface roughness of the cut surfaces is found to be too great to affect the wiring to be provided at a later stage of manufacture, the cut surfaces may be polished by a lapping process.

Then, as shown in Fig. 8, a gold (Au) film is formed on the entire cut surfaces of the laminated thermoelectric structure by a process of vacuum deposition, sputtering or electroless plating; wiring electrodes 25 are formed by patterning on the gold (Au) film using photolithographic techniques.

Subsequently, thermocouples 30 are formed by connecting, via the wiring electrodes 25, the ends of each of the first thermoelectric structures 25 to the ends of one of the second thermoelectric structures 17 adjacent to the former on the cut end surface of the laminated thermoelectric structure. A thermoelectric power generation unit is manufactured by connecting all the thermocouples 30 together in series.

In the above-mentioned manufacturing method of the thermoelectric power generation unit, the patterning of the photosensitive resin 12 of the dry film can be achieved with an accuracy of plus or minus several µm.

Also, the first thermoelectric bodies 15 and the second thermoelectric bodies 17 can be formed by plating within the openings 13 provided in the photosensitive resin 12 with the same order of patterning accuracy as in the patterning in the photosensitive resin 12, namely, within plus or minus several µm.

It can be said from the foregoing that, in comparison with the conventional machining process or the thick film process by screen printing, this process of the first embodiment can achieve much higher dimensional accuracy, and further, in the first embodiment, the thickness and composition of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 formed by a plating process are controlled with greater ease, and the preprocessing of dissolving the materials is made easier.

In the above-described manufacturing method of a thermoelectric power generation unit comprising a photolithographic process, a plating process, and a vacuum deposition process or an etching process, the manufacturing processes can be carried out on a batch basis. Consequently, the method has an advantage that a plurality of thermoelectric structures can be manufactured simultaneously.

Typically, a thermoelectric power generation unit manufactured by the method described above comprises the first thermoelectric bodies 15 and the second thermoelectric bodies 17, each individual body having a width of 150 µm and spaced at 50 µm; the total thickness thereof including the thermosetting resin 16 being 100 µm.

Assuming that the width of the substrate 10 including the thickness of the entire unit of laminated layers is 1 cm, then 2500 pairs of the thermocouples 30 can be formed on the substrate 10.

When a temperature difference of 2ºC is applied to the thermoelectric power generation unit prepared as above, an open circuit voltage of 2 V is obtained. which is sufficient to power portable electronic equipment such as a wristwatch.

Further, assuming that the length of the thermoelectric power generation unit is 2 mm, the internal impedance is 13kΩ, which shows that the unit is technically suitable for use in electronic equipment.

[Second embodiment]

Referring now to Figs. 1 and 2 and Figs. 4 to 9, the manufacturing method of a thermoelectric power generation unit according to the second embodiment of the invention will be described. Since Figs. 1 to 8 are for common use with the first embodiment as above, the second embodiment will be described with added reference to Fig. 9.

The manufacturing method of a thermoelectric power generation unit according to the second embodiment is the same as that of the first embodiment to the extent that it includes a process of forming the electrode film 11 on the substrate 10 made of a copper sheet, a process of coating the photosensitive resin 12, a patterning process, a process of coating the bottom surface of the substrate 10 with the polymer film, a process of forming the first thermoelectric bodies 15 and the second thermoelectric bodies 17, a process of peeling the polymer film from the bottom surface of the substrate 10, and a heat treatment process, as described in the case of the first embodiment with reference to Figs. 1, 2, and 7.

The manufacturing method according to the second embodiment differs from that of the first embodiment only in that in the second embodiment, a heat insulating sheet 18, as shown in Fig. 9 is used instead of the thermosetting resin 16; for the heat insulating sheet 18, a glass plate of 100 µm thickness is used and bonded to the photosensitive resin 12 and the first thermoelectric bodies 15 with an epoxy-based adhesive.

By applying the same treatment procedures as in the case of the first embodiment to a workpiece in the state shown in Fig. 9, the copper of the substrate 10 is removed using a nitric acid solution, and further the titanium of the electrode film 11 is dissolved and removed using a 1% hydrogen fluoric acid solution, whereby a first thermoelectric structure 20 is formed as shown in Fig. 4 (provided that the thermosetting resin 16 is replaced by the heat insulating sheet 18); by means of the same treatment procedure, a second thermoelectric structure is formed as shown in Fig. 5.

Subsequently, by applying the same treatment processes as in the case of the first embodiment, as shown in Figs. 6 and 8, alternate layers of the first thermoelectric structures 20 and the second thermoelectric structures 21 (provided that the thermosetting resin 16 is replaced by the heat insulating plate 18) are formed, bonded to each other, and then cut into a predetermined length.

Then, by forming wiring electrodes 25 as shown in Fig. 8, a thermoelectric power generation unit including a plurality of thermocouples 30 connected in series is completed.

In the second embodiment, which carries out the manufacturing method of a thermoelectric power generation unit according to the invention, the manufacture of a micro-sized thermoelectric power generation unit with higher accuracy ity than with conventional manufacturing processes. Also, the shape and composition of the thermoelectric power generation elements (thermocouples) are easily controlled.

Since the heat insulating sheet 18 is interposed between the first thermoelectric structure 20 and the second thermoelectric structure 21, the hardness of the thermoelectric structures is increased due to the manufacturing process according to the second embodiment as compared with the case of the first embodiment, thereby increasing the reliability of a process of dissolving the substrate 10, thereby preventing distortion and warping and enabling coping with larger substrates.

[Third embodiment]

Referring now to Figs. 1 and 3 and Figs. 10 to 13, the manufacturing method of a thermoelectric power generation unit according to the third embodiment of the invention will be described.

The manufacturing method of a thermoelectric power generation unit according to the third embodiment is the same as that described in the first embodiment with reference to Figs. 1 and 2, to the extent that it includes a process of forming the electrode film 11 on the substrate 10 made of a copper sheet, a process of coating the photosensitive resin 12, a patterning process, a process of coating the bottom surface of the substrate 10 with the polymer film, a process of forming the first thermoelectric bodies 15 and the second thermoelectric bodies 17, a process of peeling off the polymer film from the bottom surface of the substrate 10, and a heat treatment process.

As shown in Fig. 10, one substrate 10 on which first thermoelectric bodies 15 are formed and the other substrate 10 on which second thermoelectric bodies 17 are formed are bonded together with a heat insulating sheet interposed therebetween. A glass plate of 100 µm in thickness is used for the heat insulating sheet 18.

The substrate 10 with the first thermoelectric bodies 15 formed thereon is bonded to the other substrate 10 with the second thermoelectric bodies 17 formed thereon such that, as shown in Fig. 10, the surfaces of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 face the corresponding surfaces of the heat insulating sheet 18. Such bonding as stated above is carried out using an epoxy-based adhesive.

Then, the substrate 10 with the first thermoelectric bodies 15 formed thereon, which is connected to the other substrate 10 with the second thermoelectric bodies 17 formed thereon, with the heat insulating sheet 18 interposed therebetween, is immersed as a whole in a nitric acid solution, whereby all the copper for use as the material for the respective substrates 10 is dissolved and removed, and titanium for use as the material for the electrode films 11 is dissolved and removed using a 1% hydrogen fluoric acid solution. Thus, a composite thermoelectric structure 23 is formed as shown in Fig. 1.

As a next step, as shown in Fig. 12, a plurality of the assembled thermoelectric structures 23 are laminated such that the layer of the first thermoelectric bodies 15 faces the layer of the second thermoelectric bodies 17, which are bonded to Epoxy based and cut to a predetermined length.

At this time, the first thermoelectric bodies 15 are not electrically connected to the second thermoelectric bodies 17 because the respective assembled thermoelectric assemblies 23 are separated from each other by the epoxy-based insulating adhesive used for connection.

When the surface roughness of the cut surface of a thermoelectric power generating element formed as described above is so large as to affect the wiring to be provided at a later stage of processing, the cut surface of the element may be polished by a lapping process.

Then, as shown in Fig. 13, a gold (Au) film is formed on the entire cut surfaces of the element by a process of vacuum deposition, sputtering or electroless plating; wiring electrodes 25 are formed by patterning the gold (Au) film using a photolithographic technique.

Subsequently, a thermocouple 30 is formed by connecting through wiring electrodes 25 the end of one of the first thermoelectric assemblies 15 to the end of one of the second thermoelectric assemblies 17, which present themselves adjacent to each other on the cut surfaces of the element. Finally, a thermoelectric power generation unit is manufactured by connecting all the thermocouples 30 together in series.

By the manufacturing method of a thermoelectric power generation unit according to the third embodiment, a micro-sized thermoelectric power generation unit can be with higher precision than by conventional methods. In addition, the shape and composition of the thermoelectric power generating element (thermocouple) can be controlled with ease.

Furthermore, an increase in the hardness of the power generation unit is achieved due to the fact that the heat insulating plate 18 is interposed between respective composite thermoelectric structures 23, and the thickness of the heat insulating plate 18 is halved as compared with that in the case of the second embodiment, which enables the thickness of a thermoelectric power generation element to also be reduced. Thus, this method is suitable for further miniaturizing a thermoelectric power generation unit.

[Fourth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the fourth embodiment of the invention will be described below with reference to Figs. 14 to 18 and Fig. 8.

For a substrate 10' as shown in Fig. 14, a metal sheet made of titanium is used. A photosensitive resin 12 is formed on the entire surface of the substrate 10'; as the photosensitive resin 12, a photosensitive dry film 50 µm in thickness is formed by a roll coater.

As shown in Fig. 14, a pattern in the form of stripes is formed on the photosensitive resin 12 of the dry film by means of a photolithographic technique consisting of a light exposure treatment for hitting objects with light through a photomask and a development treatment for dissolving and removing underexposed portions only.

Although not shown in Fig. 14, the bottom surface of the substrate 10' is entirely coated with a Teflon-based polymer film by a spin coating process after the photosensitive resin 12 is formed.

The polymer film is coated on the bottom surface of the substrate 10' for preventing a metal deposit from being formed on the bottom surface of the substrate 10' in a state of the plating process described hereinafter.

Subsequently, the first thermoelectric bodies 15 made of a thermoelectric material are formed by plating on the substrate 10' within openings 13 of the photosensitive resin 12, as shown in Fig. 15.

A Bi-Te-Se alloy, which is an N-type semiconductor, is used as the material for the first thermoelectric bodies 15 to be formed within the openings 13 of the photosensitive resin 12.

A plating electrolyte used for forming the first thermoelectric bodies 15 made of N-type semiconductors is a nitric acid solution containing Be(NO3)3, TeO2 and SeO2. The Bi-Te-Se alloy is deposited on the substrate 10' within the openings of the photosensitive resin 12 by applying a voltage of 1 V between the substrate 10' serving as a cathode and a platinum (Pt) electrode serving as an anode.

When the first thermoelectric bodies 15 are formed by plating as stated above, the first thermoelectric bodies 15 can be deposited on the substrate 10' only in the areas within the openings formed by the photosensitive resin 12, since the underside surface of the substrate 12' is protected by the polymer film.

In the plating process for forming the first thermoelectric bodies 15, the amount of metal deposition is determined according to the amount of electric charge, which can be calculated based on the electric current consumed during electrolysis. For this reason, the thickness of the first thermoelectric bodies 15 can be easily controlled to become a required value by measuring the amount of electric charge.

The adjustment is made such that the first thermoelectric bodies 15 have the same thickness as the photosensitive resin 12, namely 50 µm.

Further, the chemical composition of the alloy can be changed by varying the ion concentration of Bi, Te and Se contained in the plating electrolyte, and the selection of the material for the first thermoelectric bodies 15 with a required output voltage and resistance value becomes possible by varying the set conditions for the ion concentration of the above-mentioned metals.

After the plating of the thermoelectric bodies 15 is completed, the polymer film is peeled off and removed from the bottom surface of the substrate 10' by toluene.

Next, the first thermoelectric bodies 15 formed on the substrate 10' are subjected to heat treatment in a nitrogen atmosphere at 350°C for one hour.

The heat treatment in a nitrogen atmosphere is used to homogenize the composition of the alloy of the first thermo electrical body so as to amplify the output of a thermoelectric power generation unit.

Then, as shown in Fig. 16, a thermosetting resin 16 made of a polyimide resin is formed by a spin coating process on the surface of both the photosensitive resin 12 and the first thermoelectric bodies 15 on the substrate 10'.

Thereafter, a heat treatment at a temperature of 150ºC or higher is applied to cure the thermosetting resin 16, namely, the polyimide resin.

Subsequently, the entire body of a thermoelectric power generating element having the photosensitive resin 12 and the first thermoelectric bodies 15 with the thermosetting resin 16 formed thereon as shown in Fig. 17 is immersed in a 1% hydrogen fluoric acid solution, whereby titanium constituting the substrate 10' is dissolved and removed.

In this dissolution treatment process, the first thermoelectric bodies 15, the photosensitive resin 12 and the thermosetting resin 16 remain as they are since all of them are insoluble in hydrogen fluoric acid, thereby forming a first thermoelectric assembly 20.

The foregoing describes the process of forming the first thermoelectric structure 20 having the first thermoelectric bodies 15, and a second thermoelectric structure 21 as shown in Fig. 5 of the first embodiment is formed by the same process as the foregoing. In this case, the process of forming second thermoelectric bodies 17 by plating with a second thermoelectric material is different from the above. The process of forming the second thermoelectric body 17 by plating with the second thermoelectric material will be described hereinafter.

After the process shown in Fig. 14 is completed, the second thermoelectric bodies 17 made of the second thermoelectric material are formed on the substrate 10' within the openings 13 provided in the thermoelectric resin 12 by means of the plating process (not shown in Fig. 14).

A Bi-Te-Sb alloy, which is a P-type semiconductor, is used as the material for the second thermoelectric bodies 17.

For forming the second thermoelectric bodies 17 made of a P-type semiconductor, the plating electrolyte uses a nitric acid solution containing Be(NO₃)₃, TeO₂ and SbCl₃. The Bi-Te-Sb alloy is deposited on the substrate 10' within the openings 13 provided in the photosensitive resin 12 by applying a voltage of 1 V between the substrate 10' serving as a cathode and a platinum (Pt) electrode serving as an anode.

In this plating process, the second thermoelectric bodies 17 are also deposited only within the openings 13 provided in the photosensitive resin 12, since the bottom surface of the substrate 10' is protected by a polymer film formed thereon.

The thickness of the second thermoelectric bodies 17 is controlled by measuring the amount of the reaction electric charge so that it is the same as the thickness of a dry film constituting the photosensitive resin 12, namely 50 µm.

The composition of the alloy is also changed by varying the ion concentration of Bi, Te and Sb, which are present in the plating electrolytes, whereby the properties of the thermoelectric bodies 17 are controlled so that they have the desired output voltage and resistance.

A second thermoelectric structure 21 is formed by the same treatment processes as those used to manufacture the first thermoelectric structure 20 described above with reference to Figs. 14 to 17, namely, a dissolving treatment of the polymer film formed on the bottom surface of the substrate, a heat treatment process, a process of coating the thermosetting resin 16, and a process of dissolving the substrate 10'.

In the next step, alternating layers of the first thermoelectric structures 20 and the second thermoelectric structures 21 are formed as shown in Fig. 18 and bonded together with an epoxy-based adhesive.

By cutting the above into a predetermined length, a laminated thermoelectric structure with the thermosetting resin 16 interposed between the first thermoelectric structures 20 and the second thermoelectric structures 21 is formed.

If the surface roughness of the cut surface after the cutting operation is found to be so great as to affect the wiring to be provided at a later stage of manufacture, the cut surfaces may be polished by a lapping process.

Then, a gold (Au) film is formed on the entire cut surfaces of the laminated thermoelectric structure by a process of vacuum deposition, sputtering or electroless plating.

Then, wiring electrodes 25 are formed by patterning the gold film using a photolithographic technique in the same manner as shown in Fig. 8 of the first embodiment.

Subsequently, a thermocouple 30 is formed by connecting the wiring electrodes 25 of the ends of one of the first thermoelectric assemblies 15 to the end of one of the second thermoelectric assemblies 17, which are shown adjacent to each other on the cut surface of the laminated thermoelectric assembly.

Finally, a thermoelectric power generation unit is manufactured by connecting all the thermocouples 30 together in series.

By the manufacturing method of a thermoelectric power generation unit according to the fourth embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than the conventional method. In addition, the shape and composition of a thermoelectric power generation element (thermocouple) can be controlled with ease.

Further, in the fourth embodiment, a titanium film serving as an electrode film 11 is not formed on a substrate 10' unlike the first to third embodiments. Therefore, the manufacturing method of a thermoelectric power generation unit according to the fourth embodiment has an additional advantage of further simplifying its manufacturing process.

[Fifth embodiment]

The manufacturing method of a thermoelectric power generation unit according to the fifth embodiment, which The method of carrying out the invention will be described below with reference to Figs. 14 and 15, Figs. 17 to 19 and Fig. 8.

In the fifth embodiment, in the same manner as in the case of the foregoing fourth embodiment, a titanium sheet is used for a substrate 10' as shown in Figs. 14 and 15, and the subsequent processes of coating and patterning with a photosensitive resin 12, coating the bottom surface of the substrate 10' with a polymer film, forming first thermoelectric bodies 15 or second thermoelectric bodies 17, and peeling the polymer film from the bottom surface of the substrate 10' are the same as those employed in the fourth embodiment.

In the next step, contrary to the case of the fourth embodiment, a heat insulating sheet 18 is formed instead of the thermosetting resin 16 as shown in Fig. 19 on a photosensitive resin 12 and first thermoelectric bodies 15 provided on the substrate 10'. For the heat insulating sheet 18, a glass plate of 100 µm thick is used and bonded to the surface of the photosensitive resin 12 and the first thermoelectric bodies 15 by a bonding agent.

Then, as shown in Fig. 17, the titanium constituting the substrate 10' is dissolved and removed using a 1% hydrofluoric acid solution to obtain a first thermoelectric structure. Further, a second thermoelectric structure 21 is formed by the same treatment process.

Subsequently, as shown in Fig. 18, alternating layers of the first thermoelectric structures 20 and the second thermoelectric structures 21 are formed, bonded together and cut, thereby forming a laminated thermoelectric structure.

Then, a gold (Au) film is formed on the entire cut surfaces of the laminated thermoelectric structure by a process of vacuum deposition, sputtering or electroless plating, and wiring electrodes 25 are formed by patterning the gold (Au) film using a photolithography technique in the same manner as shown in Fig. 8 in the first embodiment, thereby forming a thermoelectric power generation unit.

By the manufacturing method of a thermoelectric power generation unit according to the fourth embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than the conventional methods. In addition, the shape and composition of the thermoelectric power generation element (thermocouple) can be controlled with ease.

In the fifth embodiment in which a heat insulating sheet 18 is inserted between the first thermoelectric structures 20 and the second thermoelectric structures 21, this manufacturing method of a thermoelectric power generation unit according to the invention can be applied to substrates having larger dimensions.

[Sixth Embodiment}

The manufacturing method of a thermoelectric power generation unit according to the sixth embodiment of the invention will be described hereinafter with reference to Figs. 14 and 15, Fig. 20 and Figs. 11 to 13.

In the sixth embodiment, in the same manner as in the aforementioned fourth embodiment, a titanium sheet is used for a substrate 10' as shown in Figs. 14 and 15, and the subsequent processes of coating and coating patterning with a photosensitive resin 12, coating the bottom surface of the substrate 10' with a polymer film, forming first thermoelectric body 15 or second thermoelectric body 17, peeling the polymer film from the bottom surface of the substrate 10' and heat treatment are the same as those applied to the fourth embodiment.

As shown in Fig. 20, one substrate on which first thermoelectric bodies 15 are formed and the other substrate on which second thermoelectric bodies 17 are formed are bonded together with a heat insulating sheet interposed therebetween; a glass plate of 100 µm in thickness is used for the heat insulating sheet 18.

The substrate 10' with the first thermoelectric bodies 15 formed thereon is bonded to the other substrate 10' with the second thermoelectric bodies 17 formed thereon such that the surfaces of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 face the corresponding surfaces of the heat insulating sheet 18 using an epoxy-based adhesive.

Then, the substrate 10' with the first thermoelectric bodies 15 formed thereon, which is bonded to the other substrate 10' with the second thermoelectric bodies 17 formed thereon with the heat insulating sheet 18 interposed therebetween, is immersed in a 1% hydrogen fluoric acid solution, thereby dissolving and removing titanium used as the material of the respective substrates 10'. Thus, a composite thermoelectric structure 23 is formed as shown in Fig. 11 of the aforementioned third embodiment.

In the next step, as shown in Fig. 12, a plurality of the assembled thermoelectric structures 23 are laminated such that the layer of the first thermoelectric bodies 15 is opposed to the layer of the second thermoelectric bodies 17, they are bonded together using an epoxy-based adhesive, and cut into a predetermined length.

At this point, the first thermoelectric bodies 15 are not bonded to the second thermoelectric bodies 17, since respective composite thermoelectric assemblies 23 are separated from each other by the insulating epoxy-based adhesive used for bonding, although this is not shown in Fig. 12.

When the surface roughness of the cut surfaces of a thermoelectric power generating element formed as described above is so large as to affect the wiring provided at a later stage of processing, the cut surfaces of the elements may be polished by a lapping process.

Then, as shown in Fig. 13, a gold (Au) film is formed on the entire cut surfaces of the element by a method of vacuum deposition, sputtering or electroless plating; wiring electrodes 25 are formed by patterning the gold film using a photolithographic technique.

Subsequently, a thermocouple 30 is manufactured by connecting through the wiring electrodes 25 the ends of one of the first thermoelectric assemblies 15 to the end of one of the second thermoelectric assemblies 17, which face adjacent to each other on the cut surfaces of the element. Finally, a thermoelectric power generation unit is manufactured by connecting all the thermocouples 30 together in series.

By the manufacturing method of a thermoelectric power generation unit according to the sixth embodiment, a micro-sized thermoelectric power generation unit can be manufactured with higher accuracy than the conventional methods. In addition, the shape and composition of the thermoelectric power generation element (thermocouple) can be controlled with ease.

Furthermore, an increase in the hardness of the power generation unit is achieved due to the fact that the heat insulating sheet 18 is inserted between the respective composite thermoelectric structures 23, and as a result, the thickness of the heat insulating sheet 18 can be reduced to half of the case of the fifth embodiment, thereby enabling the thickness of the laminated thermoelectric power generation elements to also be reduced. Thus, the method is suitable for further miniaturization of a thermoelectric power generation unit.

[Seventh Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the seventh embodiment of the invention will be described hereinafter with reference to Figs. 21 to 28.

As shown in Fig. 21, a copper sheet whose upper surface is coated with an insulating film (not shown), for example, SiO2 film, is used as the substrate 10.

The insulating film formed of SiO2 is a film provided for preventing a short circuit between two electrode films to be formed in a later stage of processing, which would be caused by the copper of the substrate 10.

In the next step, a titanium film of 500 nm in thickness, serving as an electrode film, is formed on the entire upper surface of the substrate 10 by a vacuum deposition process.

Then, patterning of the titanium film, namely, an electrode film, is performed using photolithographic techniques and etching techniques so as to produce a planar pattern in the shape substantially resembling teeth of two combs provided opposite to each other with each tooth mutually interposed, thereby forming a first electrode film 31 and a second electrode film 32. Fig. 22 is a plan view showing the shape of the planar pattern of the first electrode film 31 and the second electrode film 32.

Subsequently, a photosensitive resin 12 is formed on the entire surface of the substrate 10 on which the first electrode film 31 and the second electrode film 32 are provided; as the photosensitive resin 12, a photosensitive dry film having a thickness of 50 µm is formed by a roll coater.

As shown in Fig. 23, the photosensitive resin 12 is formed in gap portions between the first electrode film 31 and the second electrode film 32 using a photolithographic technique so that a pattern in the form of stripes is made.

After the photosensitive resin 12 is formed, the bottom surface of the substrate 10 is entirely coated with a Teflon-based polymer film using a spin coating process, although this is not shown in Fig. 23.

Then, as shown in Fig. 24, first thermoelectric bodies 15 made of a first thermoelectric material are are first formed on the first electrode film 31 by plating within openings 13 of the photosensitive resin 12.

A Bi-Te-Se alloy, which is an N-type semiconductor, is used as the material for the first thermoelectric bodies 15, which are formed on the first electrode film 31.

A plating electrolyte used for forming the first thermoelectric bodies 15 made of an N-type semiconductor is a nitric acid solution containing Bi(NO₃)₃, TeO₂, and SeO₂.

The Bi-Te-Se alloy is deposited on the first electrode film 31 within the openings 13 of the photosensitive resin 12 by applying a voltage of 1 V between the first electrode film 31 serving as a cathode and a platinum (Pt) electrode serving as an anode.

The thickness of the first thermoelectric bodies 15 is controlled by the amount of the reaction electric charge and is set to be substantially the same as that of the photosensitive resin 12, namely 50 µm.

Subsequently, second thermoelectric bodies 17 made of a second thermoelectric material are formed on the second electrode film 32 within the openings 13 provided in the thermoelectric resin 12 by means of the plating process.

A Bi-Te-Sb alloy, which is a P-type semiconductor, is used as the material for the second thermoelectric bodies 20 made of the second thermoelectric material, which are formed on the second electrode film 32.

A plating electrolyte used for forming the second thermoelectric bodies 17 made of a P-type semiconductor is a nitric acid solution containing Bi(NO₃)₃, TeO₂ and SbCl₃.

The Bi-Te-Sb alloy is deposited on the second electrode film 32 within the openings 13 provided in the photosensitive resin 12 by applying 1 V between the second electrode film 32 serving as a cathode and a platinum (Pt) electrode serving as an anode.

The thickness of the second thermoelectric bodies 17 is controlled by the measure of the amount of the reaction electric charge so as to be the same as that of the dry film constituting the photosensitive resin 12, namely 50 µm.

After applying a plating process twice to form the first thermoelectric bodies 15 and the second thermoelectric bodies 17, the polymer film formed on the bottom surface is dissolved and removed by toluene. Thereafter, the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are heat-treated in a nitrogen atmosphere at 350°C for one hour.

Then, as shown in Fig. 25, a thermosetting resin 16 made of polyimide resin is formed on the upper surface of the first thermoelectric bodies 15, the second thermoelectric bodies 17 and the photosensitive resin 12 using a spin coating process.

Then, the polyimide resin of the thermosetting resin 16 is cured by applying a heat treatment at a temperature of 150ºC or higher. Subsequently, a thermoelectric assembly is formed including the first thermoelectric bodies 15, the second thermoelectric bodies 17 and the photosensitive resin 12 formed by the thermosetting resin 16. formed thereon is immersed in a nitric acid solution, thereby dissolving all the copper constituting the substrate 10, and then immersed in a 1% hydrogen fluoric acid solution, which dissolves and removes the SiO₂ film as the insulating film and the titanium film constituting the first electrode film 31 and the second electrode film 32.

After the above-mentioned dissolving process, the first thermoelectric bodies 15, the second thermoelectric bodies 17, the photosensitive resin 12 and the thermosetting resin 16 remain as they are since they are all insoluble in nitric acid and hydrofluoric acid. As shown in Fig. 26, a thermoelectric assembly 24 is thus formed.

Then, a plurality of the thermoelectric assemblies 24 are stacked in multiple layers and bonded together by an epoxy-based adhesive; by cutting into a length as desired, a laminated thermoelectric assembly having the plurality of the thermoelectric assemblies 24 stacked in multiple layers is manufactured as shown in Fig. 27.

If the surface roughness of the cut end surface of an element is found to be so great as to affect the wiring to be provided at a later stage of manufacture, the cut surfaces may be polished by a lapping process.

As shown in Fig. 28, a gold (Au) film is formed on the entire cut end surface of the laminated thermoelectric structure by a process of vacuum deposition, sputtering or electroless plating.

Then, wiring electrodes 25 are formed by patterning the gold film using photolithographic techniques.

Subsequently, a thermocouple 30 is formed by connecting the wiring elements 25 of the end of the corresponding first thermoelectric body 15 to the end of the corresponding second thermoelectric body 17 which are adjacent to each other on the cut end surface of a thermoelectric power generating element.

Finally, a thermoelectric power generation unit is manufactured by connecting all the thermocouples 30 together in series.

In Fig. 28, a thermocouple is formed by connecting one of the first thermoelectric body 15 and one of the second thermoelectric bodies 17 adjacent to each other within a thermoelectric assembly 24; also, a thermocouple may be formed by connecting one of the thermoelectric assemblies 24 to another thermoelectric assembly 24 adjacent to the former.

By the manufacturing method of a thermoelectric power generation unit according to the seventh embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than the conventional methods. In addition, the shape and composition of a thermoelectric power generation element (thermocouple) can be controlled with ease.

[Eighth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the eighth embodiment of the invention will be described hereinafter with reference to Figs. 21 to 24 and Figs. 26 to 29.

In the eighth embodiment, the manufacturing process is the same as that of the seventh embodiment, as shown in Fig. 21 to 24, in that a copper sheet coated with an insulating layer of SiO₂ is used as the substrate 10, and the steps of processing include: forming an electrode film made of titanium on the substrate 10; forming a first electrode film 31 and a second electrode film 32 by patterning; coating with a photosensitive resin 12 and patterning the same; coating the bottom surface of the substrate 10 with a polymer film; forming first thermoelectric bodies 15 and second thermoelectric bodies 17; peeling the polymer film from the bottom surface of the substrate 10; and applying a heat treatment.

The next step differs from the seventh embodiment in that, as shown in Fig. 29, a heat insulating sheet 18 is used instead of the thermosetting resin 16. A glass plate of 100 µm in thickness is used as the heat insulating sheet 18 and bonded to the upper surfaces of the first thermoelectric bodies 15, the second thermoelectric bodies 17 and the photosensitive resin 12.

Then, as shown in Fig. 26, a thermoelectric assembly 24 (using the heat insulating sheet 18 instead of the thermosetting resin 16) is formed by dissolving the copper constituting the substrate 10 in a nitric acid solution and further dissolving and removing the SiO2 film as the insulating film, the first electrode film 31 and the second electrode film 32 in a 1% hydrogen fluoride acid solution.

Subsequently, a plurality of the thermoelectric structures 24 are stacked in multiple layers one after another, bonded together, and cut; by forming wiring electrodes 25 on the cut end faces, a thermoelectric power generation unit is manufactured.

By the manufacturing method of a thermoelectric power generation unit according to the eighth embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than the conventional methods. In addition, the shape and composition of a thermoelectric power generation element (thermocouple) can be controlled with ease.

Furthermore, the manufacturing method of a thermoelectric generation unit according to the eighth embodiment can be applied to a substrate of larger size since the thermoelectric structures 24 have the heat insulating plates 28 interposed therebetween.

[Ninth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the ninth embodiment of the invention will be described hereinafter with reference to Figs. 22 to 25 and Figs. 30 to 32.

In the ninth embodiment, the manufacturing method is the same as that of the seventh embodiment shown in Figs. 22 to 25 to the extent that a copper plate coated with an insulating film of SiO₂ is used for a substrate 10, and the subsequent processing steps include: forming an electrode film made of titanium on the substrate 10, forming a first electrode film 31 and a second electrode film 32 by patterning, coating with a photosensitive resin 12 and patterning it, coating the bottom surface of the substrate 10 with a polymer film, forming first thermoelectric bodies 15 and second thermoelectric bodies 17, peeling off the polymer film from the bottom surface of the substrate 10 and applying a heat treatment,

In the next step, two substrates each having the first thermoelectric bodies 15 and the second thermoelectric bodies 17 formed thereon are bonded together with a heat insulating sheet 18 interposed therebetween. For the heat insulating sheet 18, a glass plate of 100 µm in thickness is used.

The two substrates on which the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are formed are bonded to each other by an epoxy-based adhesive by providing the respective substrates such that the surface on which the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are formed of each substrate faces the heat insulating sheet 18.

Subsequently, a composite thermoelectric structure 25 as the thermoelectric body 15 and the second thermoelectric bodies 17 formed thereon, which are bonded together with the heat insulating sheet 18 interposed therebetween, is formed, and thereafter, after dissolving the insulating film of SiO₂ and the titanium constituting the first electrode film 21 and the second electrode film 32, the two substrates are immersed in a 1% hydrogen fluoric acid solution.

Subsequently, as shown in Fig. 32, a plurality of the assembled thermoelectric assemblies 26 are stacked in multiple layers, bonded together by an epoxy-based adhesive, and cut into a desired length.

At this time, the first thermoelectric bodies 15 are not connected to the second thermoelectric bodies 17, since the corresponding assembled thermoelectric structures 26 are separated from each other by means of the insulating adhesive on Epoxy base used for bonding, although this is not shown in Fig. 32.

When a surface roughness of the cut surfaces of the thermoelectric power generating element formed as described above is so large as to affect the wiring provided in a later stage of processing, the cut surfaces of the element may be polished by a lapping process.

As shown in Fig. 28, a gold (Au) film is formed on the entire cut surfaces of the element by a process of vacuum deposition, sputtering or electroless plating; wiring electrodes 25 are formed by patterning the gold film using photolithographic techniques.

A thermocouple 30 is manufactured by connecting the respective first thermoelectric bodies 15 to the respective thermoelectric bodies 17 appearing adjacent to each other on the cut surface through the wiring electrodes 25.

By connecting the thermocouples 30 together in series, a thermoelectric power generation unit is manufactured.

By the manufacturing method of a thermoelectric power generation unit according to the ninth embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than the conventional methods. In addition, the shape and composition of a thermoelectric power generation element can be controlled with ease.

Furthermore, an increase in the hardness of a power generation unit is achieved due to the fact that the heat insulating Sheet 18 can be inserted between the respective assembled thermoelectric structures 26, and as a result, the thickness of the heat insulating sheet 18 can be halved as compared with that in the case of the eighth embodiment, whereby the thickness of the laminated thermoelectric power generation elements can be reduced. Thus, this method is suitable for further miniaturization of a thermoelectric power generation unit.

[Tenth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the tenth embodiment of the invention will be described hereinafter with reference to Figs. 21 to 25 and Figs. 33 and 34.

As shown in Fig. 21, a copper sheet whose upper surface is coated with an insulating film, for example, a SiO₂ film, is used for a substrate 10.

The insulating film made of SiO2 is a film intended to prevent a short circuit between two electrode films to be formed during a later step of processing, which would be caused by the copper in the substrate 10.

In the next step, a first electrode film 31 and a second electrode film 32 are formed on the entire upper surface of the substrate 10 by depositing a titanium film in a thickness of 500 nm by a vacuum deposition process.

A pattern is formed in the titanium film using photolithographic techniques and etching techniques to produce a planar pattern in shape substantially similar to the teeth of two combs arranged opposite each other and having their teeth interposed between each other. are seen, whereby the first electrode film 31 and the second electrode film 32 are formed.

Fig. 22 is a plan view showing the shape of the planar pattern of the first electrode film 31 and the second electrode film 32; the pattern in the shape substantially resembling the teeth of the combs facing each other is formed so that a gap portion is created between the first electrode film 31 and the second electrode film 32.

Subsequently, a photosensitive resin 12 is formed on the entire surface of the substrate 10 on which the first electrode film 31 and the second electrode film 32 are provided; as the photosensitive resin 12, a photosensitive dry film having a thickness of 50 µm is formed by a roll coater.

As shown in Fig. 23, the photosensitive resin 12 is formed in the gap region between the first electrode film 31 and the second electrode film 32 using the photolithographic techniques such that patterning is performed in the form of stripes.

After the photosensitive resin 12 is formed, the bottom surface of the substrate 10 is coated entirely with a Teflon-based polymer film using a spin coating process, although this is not shown in Fig. 23.

Subsequently, first thermoelectric bodies 15 made of a first thermoelectric material are formed by plating on the first electrode film 31 within the openings of the photosensitive resin 12, as shown in Fig. 25.

A Bi-Te-Se alloy, which is an N-type semiconductor, is used as the material for the first thermoelectric bodies 15, which are formed on the first electrode film 31.

A plating electrolyte used for forming the first thermoelectric bodies 15 made of an N-type semiconductor is a nitric acid solution containing Bi(NO3)3, TeO2 and SeO2. The Bi-Te-Se alloy is deposited on the first electrode film 31 within the openings of the photosensitive resin 12 by applying a voltage of 1 V between the first electrode film 31 serving as a cathode and a platinum (Pt) electrode serving as an anode.

The thickness of the first thermoelectric bodies 15 is controlled by the amount of the reaction electric charge and is set to be substantially the same as that of the photosensitive resin 12, namely 50 µm.

Subsequently, second thermoelectric bodies 17 made of a second thermoelectric material are formed on a second electrode film 32 by means of a plating process.

A Bi-Te-Sb alloy, which is a P-type semiconductor, is used as the material for the second thermoelectric bodies 17.

A plating electrolyte used for forming the second thermoelectric bodies 17 made of a P-type semiconductor is a nitric acid solution containing Bi(NO3)3, TeO2 and SbCl3; the Bi-Te-Sb alloy is deposited on the second electrode film 32 within the openings 13 provided in the photosensitive resin 12 by applying 1 V between the second electrode film 32 serving as a cathode and a platinum (Pt) electrode serving as an anode.

The thickness of the second electrode film 32 is controlled by measuring the amount of the reaction electric charge to be substantially the same as that of the photosensitive resin 12, namely 50 µm.

After applying a plating process twice to form the first thermoelectric bodies 15 and the second thermoelectric bodies 17, the polymer film formed on the bottom surface of the substrate 10 is dissolved and removed by toluene. Thereafter, the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are heat-treated in a nitrogen atmosphere at 350°C for one hour.

Then, as shown in Fig. 25, a thermosetting resin 16 made of polyimide resin is formed on the upper surface of the first thermoelectric bodies 15, the second thermoelectric bodies 17 and the photosensitive resin 12 using a spin coating method.

Then, the polyimide resin of the thermosetting resin 16 is cured by applying a heat treatment at a temperature of 150°C or higher.

All of the copper forming the substrate 10 is dissolved by immersing an entire body of a thermoelectric assembly thus formed in a nitric acid solution.

After the process of dissolving the substrate 10, the first thermoelectric bodies 15, the second thermoelectric bodies 17, the photosensitive resin 12 and the thermosetting resin 16 remain as they are, since they are all insoluble in the nitric acid solution.

Subsequently, the insulating film consisting of the SiO₂ film and the first electrode film 31 and the second electrode film 32, both consisting of the titanium film, are mentioned films remained until now are dissolved and removed using a hydrogen fluoride acid so that a plating initiation surface 33 of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 is exposed as shown in Fig. 33.

Then, a gold (Au) film is formed on the plating initiation surface 33 by the vacuum deposition process, and patterning is provided on the gold film by the photolithographic process and the etching process so that wiring electrodes 35 are formed in such a manner as to alternately connect one of the first thermoelectric bodies 15 to one of the second thermoelectric bodies 17 adjacent to the former, thereby forming a thermocouple 30'. Through the above-described treatments and processes, a thermoelectric assembly 27 having many thermocouples is formed.

Thereafter, a plurality of thermoelectric structures 27 are stacked in multilayers and bonded together by an epoxy-based adhesive.

Finally, a thermoelectric power generation unit is manufactured by connecting all of the thermocouples 30' together in series.

By this manufacturing method, a thermoelectric power generation unit according to the tenth embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than by the conventional methods. In addition, the shape and composition of a thermoelectric power generation element (thermocouple) can be controlled with ease.

[Eleventh embodiment]

The manufacturing method of a thermoelectric power generation unit according to the eleventh embodiment of the invention will be described hereinafter with reference to Figs. 33, 34 and others.

The manufacturing method according to the eleventh embodiment of the invention is the same as that of the tenth embodiment to the extent that a copper sheet whose upper surface is coated with an insulating film made of SiO₂ is used for a substrate 10 and comprises the following processing steps of forming an electrode film of titanium, forming a first electrode film 31 and a second electrode film 32 by patterning; coating with a photosensitive resin 12 and patterning therein, coating the lower surface of a substrate 10 with a polymer film, forming first thermoelectric bodies 15 and second thermoelectric bodies 17, peeling the polymer film from the lower surface of the substrate 10, and applying a heat treatment.

In the next step of processing, the eleventh embodiment differs from the tenth embodiment in that a heat insulating sheet 18 made of glass is used instead of the thermosetting resin 16, as shown in Fig. 29. The heat insulating sheet 18 having a thickness of 100 µm is bonded to the upper surfaces of the first thermoelectric bodies 15, the second thermoelectric bodies 17 and the photosensitive resin 12 by an epoxy-based adhesive.

Subsequently, the copper sheet constituting the substrate 10 is dissolved in a nitric acid solution and removed; further, the insulating film consisting of the SiO₂ film and the first electrode film 31 and the second electrode film 32, both made of titanium, are dissolved in a 1% hydrogen fluoric acid solution and removed. Then, a gold (Au) film is formed on the plating initiation surface 33 and the coating is removed. star therein, thereby forming wiring electrodes 35 in the same manner as shown in Fig. 33. Thus, a thermoelectric structure 27 is formed.

Thereafter, a plurality of the thermoelectric structures 27 are stacked in multiple layers and connected to each other, thereby forming a thermocouple in the same manner as shown in Fig. 34 (except that the heat insulating sheet 18 is used instead of the thermosetting resin 16); a thermoelectric power generation unit is manufactured by connecting all the thermocouples together in series.

By the manufacturing method, a thermoelectric power generation unit according to the eleventh embodiment, a micro-sized thermoelectric power generation unit can be formed with higher accuracy than by the conventional methods. In addition, the shape and composition of a thermoelectric power generation element can be controlled with ease.

Furthermore, since the heat insulating sheets 18 are interposed between the majority of the thermoelectric structures 27, this method can be applied to substrates of larger dimensions.

[Twelfth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the twelfth embodiment of the invention will be described hereinafter with reference to Figs. 35, 36 and others.

The manufacturing method according to the twelfth embodiment of the invention is the same as that of the tenth embodiment to the extent that a copper sheet whose upper surface is coated with an insulating film made of SiO₂ is used for a Substrate 10 is used, and comprising the following processing steps of forming an electrode film of titanium, forming a first electrode film 31 and a second electrode film 32 by patterning, coating with a photosensitive resin 12 and patterning therein, coating the bottom surface of the substrate 10 with a polymer film, forming first thermoelectric bodies 15 and second thermoelectric bodies 17, peeling the polymer film from the bottom surface of the substrate 10 and applying a heat treatment.

In the next step, as shown in Fig. 30, two substrates each having the first thermoelectric bodies 15 and the second thermoelectric bodies 17 formed thereon are bonded together with a heat insulating sheet 18 interposed therebetween. For the heat insulating sheet 18, a glass plate having a thickness of 100 µm is used.

The two substrates on which the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are formed are bonded to each other by an epoxy-based adhesive in which the respective substrates are provided so that the surface on which the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are formed of each substrate faces the heat insulating sheet 18.

Subsequently, copper constituting the substrate 10 is dissolved and removed by immersing an element as a whole comprising the first thermoelectric bodies 15 and the second thermoelectric bodies 17 and connected with the heat insulating sheet interposed therebetween in a nitric acid solution, and then the insulating film made of the SiO₂ film and the first electrode film 31 and the second electrode film 32 both made of the titanium film are all the above-mentioned films remaining up to now are dissolved and removed by using a hydrogen fluoric acid, so that a plating initiation surface 33 of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 is exposed as shown in Fig. 33.

Then, a gold (Au) film is formed by the vacuum deposition process on the plating initiation surface 33 thus exposed, and patterning is provided on the gold film by the photolithographic process and the etching process so that wiring electrodes 35 are formed in such a manner as to alternately connect one of the first thermoelectric bodies 15 to one of the second thermoelectric bodies 17 adjacent to the former, thereby forming a thermocouple 30'. Through the above-described treatments and processes, a thermoelectric assembly 28 is formed.

Thereafter, a plurality of the thermoelectric assemblies 28 are stacked in multiple layers and bonded together by an epoxy-based adhesive, as shown in Fig. 36.

At this stage, the first thermoelectric bodies 15 are not electrically connected to the second thermoelectric bodies 17, since the respective composite thermoelectric assemblies 28 are separated from each other by means of the epoxy-based adhesive used for the connection. Finally, a thermoelectric power generation unit is manufactured by connecting all the thermocouples 30' together in series.

By the manufacturing method of a thermoelectric power generation unit according to the twelfth embodiment, a micro-sized thermoelectric power generation unit can be manufactured with higher accuracy than by the conventional methods In addition, the shape and composition of a thermoelectric power generation element can be easily controlled.

Further, an increase in hardness of a power generation unit is achieved due to the fact that the heat insulating sheet 18 is interposed between the respective composite thermoelectric bodies.

Furthermore, an increase in the hardness of a power generation unit is achieved due to the fact that the heat insulating sheet 18 is inserted between the respective composite thermoelectric structures 28, and as a result, the thickness of the heat insulating sheet 18 can be reduced to half of the case of the twelfth embodiment, whereby the thickness of the laminated thermocouples can be reduced. Thus, this method is suitable for further miniaturization of the thermoelectric power generation unit.

In the foregoing embodiments one to twelve, a copper sheet or a titanium sheet is used as the material for the substrate 10, but other materials which do not attack the thermoelectric process materials dry film or polyimide but are soluble by the etching process may be substituted for the copper sheet or titanium sheet.

Either metal materials such as a steel sheet, a nickel sheet, a galvanized iron sheet, aluminum sheet, brass sheet and the like, or ceramic materials such as a glass plate, an aluminum sheet and the like can be used as the material for the substrate 10.

Also, examples in which a titanium film is used to form the electrode film 11, the first electrode film 31 or the second electrode film 32 on the substrate 10 are described above. Other materials for a metal film, if they are insoluble in a plating solution, a titanium film used for forming the electrode film, the first electrode film 31 or the second electrode film 32 may be substituted; an Au film, a Pt film, a Pd film, a Ta film or the like are possible alternative materials.

Also, in the first to twelfth embodiments, the use of an Au film for forming the wiring electrodes 25 is described.

However, not only an Au film but also other metal materials such as a Cu film, Al film, Ni film, Fe film and the like may be used to form the wiring electrodes 25.

In the foregoing embodiments, the process of forming the wiring electrodes 25 by forming a film first and patterning thereon by means of the photolithographic techniques and etching techniques is described. However, another process of forming an electrode pattern by first covering the entire surface except for the areas where the electrodes are to be formed with a special masking material and then removing a metal mask after a metal film is formed on the entire surface, which is called a mask deposition process, can also be applied to the manufacturing method of the invention.

Still another process of forming the wiring electrodes 25 such as a printing process or a process of adhering to the surface of a film formed on another material in a sheet form and patterned in the shape of the wiring electrodes may be applicable.

Also, in the foregoing embodiments, a photosensitive dry film is used for the photosensitive resin 12 which is formed in the course of plating with the thermoelectric materials for the first thermoelectric bodies 15 and the second thermoelectric body 17 is required, but a photosensitive polyimide other than a dry film may be used for the photosensitive resin.

If the thickness on the order of 10 µm of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 is sufficient to meet the requirements, a rubber-based photoresist or a cinnamic acid-based photoresist may be used for the photosensitive resin used when the thermoelectric materials are plated.

In the foregoing embodiments, the use of polyimide is described for the thermosetting resin 16, however, an epoxy-based adhesive or an acrylic resin may be used for the thermosetting resin in addition to the polyimide.

Besides the spin coating process described as the method of forming the thermosetting resin 16, a spray coating process, a roll coating process, or a film-sticking process or the like may be used.

Also, in addition to the glass plate used for the heat insulating sheet 18, a ceramic sheet, a plastic sheet or the like, which are low in thermal conductivity and are in a thin sheet form but have high resistance to deformation, can be used for the heat insulating sheet 18.

Regarding the thermoelectric materials, Bi-Te-Se alloy is used for the N-type semiconductor, and Bi-Te-Sb alloy is used for the P-type semiconductor in the foregoing embodiments. However, the N-type semiconductor and the P-type semiconductor can be produced by varying the concentration of Bi to that of Te without mixing either Se or Sb.

Also, materials other than those mentioned above may be used as the thermoelectric materials for forming the first thermoelectric bodies 15 and the second thermoelectric bodies 17 if the materials are suitable for deposition by plating.

[Thirteenth Embodiment]

The manufacturing method of a thermoelectric power generation unit according to the thirteenth embodiment of the invention will be described hereinafter with reference to Figs. 37 to 45.

First, as shown in Fig. 37, a copper sheet is used to form a substrate 10, and an electrode film 11 is formed on the entire surface of the substrate 10 by forming a titanium (Ti) film of 500 nm in thickness by a vacuum deposition process.

The electrode film 11 consisting of the titanium film serves to protect the copper sheet forming the substrate 10 from attack by a plating solution during the process described hereinafter.

Then, two layers of a photosensitive dry film each being 50 µm thick are formed as a photosensitive resin 12 on the substrate 10 by a roll coater so that the total thickness of the photosensitive resin 12 becomes 100 µm.

Then, using photolithographic techniques, a combination of a so-called exposure treatment with a so-called development treatment is carried out, in which a light-sensitive film is irradiated through a photomask and exposed to light in such a way that only unexposed areas are dissolved. and are removed, a pattern in the form of stripes is provided on the photosensitive resin 12 consisting of the dry film as shown in Fig. 1, thereby forming a photosensitive resin 12a having a first pattern in the form of stripes.

The photosensitive resin 12a having a pattern in the form of stripes forms openings on the electrode film 11, namely areas that are dissolved and removed by means of the photolithographic techniques, and unopened surface areas, namely areas that have not yet been dissolved and removed by means of the photolithographic techniques.

As shown in Fig. 44, the first pattern is formed in the form of stripes such that the width Wa of the respective openings of the photosensitive resin 12a is larger than the width Wb corresponding to the unopened surface areas thereof, in other words, Wa is 150 µm while Wb is 50 µm.

After patterning the photosensitive resin 12 as shown in Fig. 37, a Teflon-based polymer film 19 is formed on the entire bottom surface of the substrate 10 using a spin coating process as shown in Fig. 38.

The polymer film 19 is formed on the bottom surface of the substrate for preventing metal deposits by platings which may be formed on the bottom surface of the substrate 10 at a later stage of processing.

Subsequently, first thermoelectric bodies 15 made of a first thermoelectric material are formed inside the openings 13a of the photosensitive resin 12a by means of a plating process.

A Bi-Te-Se alloy, which is an N-type semiconductor, is used as the material for the first thermoelectric bodies 15.

As a plating electrolyte, a nitric acid solution containing Bi(NO3)3, TeO2 and SeO2 is used. The first thermoelectric bodies 15 made of the Bi-Te-Se alloy are deposited on the electrode film 11 within the openings 13a of the photosensitive resin 12a by applying a voltage of 1 V between the electrode film 11 serving as a cathode and a platinum (Pt) electrode serving as an anode.

During the plating process, the underside of the substrate 10 is protected by the polymer film 19. Consequently, the first thermoelectric bodies 15 are deposited only within the openings 13a of the photosensitive resin 12a.

In the plating process, the amount of metal deposition is determined by the amount of electric charge, which can be calculated from the electric current consumed during the time the electrolysis takes place. Therefore, the thickness of the first thermoelectric bodies 15 is easily controlled by measuring the amount of electric charge.

In this case, the thickness of the first thermoelectric bodies 15 is set to be half the thickness of the photosensitive resin 12a already formed by patterning.

Further, the chemical composition of the alloy constituting the first thermoelectric bodies 15 can be changed by varying the ion concentration of Bi, Te, and Se, respectively. Consequently, a material capable of producing a desired output voltage and low resistance will be selected by setting the setting conditions as described above. Thus, a thermoelectric structure 41 is formed as shown in Fig. 39.

By applying substantially the same treatment process as that used in the manufacturing process of the first thermoelectric structure 41, a second thermoelectric structure 42 is formed as shown in Fig. 40.

Hereinafter, a process of forming the second thermoelectric structure 42 will be mainly described in the area in which it differs from the process of forming the first thermoelectric structure 41.

The process of forming the second thermoelectric assembly 42 is the same as that of the first thermoelectric assembly 41 as described with reference to Figs. 37, 38 and 44 up to a point where patterning in the form of stripes is performed on the photosensitive resin and the polymer film is formed.

In the process of forming the second thermoelectric structure 42, patterning is performed on a photosensitive resin 12b, namely, a second pattern in the form of stripes such that the second pattern in the form of stripes is identical to the first pattern in the form of stripes on the photosensitive resin 12a in terms of the width of the respective openings Wa, the width of the respective unopened surface areas Wb, and the thickness.

Thus, the first thermoelectric structure 41 and the second thermoelectric structure 42 have elements necessary for co-production, contributing to the improved productivity in the manufacture of thermoelectric power generation units, wherein the dimensions of the second pattern in the form of stripes on the photosensitive resin 12b are the same as those of the first pattern in the form of stripes.

In addition, since the pattern in the form of stripes provided on the photosensitive resin 12b is identical to the first pattern in the form of stripes on the photosensitive resin 12a, the first thermoelectric assembly 41 can be well-fitted into the second thermoelectric assembly 42 as described later herein, whereby the processing can proceed without warping and higher efficiency in the manufacture of thermoelectric power generation units can be achieved.

The process of forming the second thermoelectric structure 42 is different from that for the first thermoelectric structure 41 with respect to a process of plating the thermoelectric material for the second thermoelectric bodies 17, which will be described below.

After completion of the same process as shown in Fig. 38, the second thermoelectric bodies 17 made of a second thermoelectric material are formed by a plating process within openings 13b of the photosensitive resin 12b having the second pattern in the form of stripes as shown in Fig. 40. A Bi-Te-Sb alloy, which is a P-type semiconductor, is used to form the second thermoelectric bodies 17.

A phosphoric acid solution containing Bi(NO3)3, TeO2 and SbCl3 is used as a plating electrolyte. Each of the second thermoelectric bodies 17 made of the Bi-Te-Sb alloy is deposited on the electrode film 11 within one of the openings 13b provided in the photosensitive resin 12b by applying 1 V between the electrode film 11 serving as a cathode and a platinum (Pt) electrode serving as an anode.

Since the rear surface of the substrate 10 is protected by the polymer film 19, the second thermoelectric bodies 17 are deposited only within the openings 13b of the photosensitive resin 12b. The thickness of the second thermoelectric bodies 17 is controlled to be half the thickness of the photosensitive resin 12b, namely 50 µm, by measuring the amount of the reaction electric charge.

Furthermore, the chemical composition of the alloy constituting the second thermoelectric bodies 17 can be changed by varying the ion concentration of Bi, Te or Sb, whereby the properties of the alloys can be controlled so that they can produce a desired output voltage and have a low resistance.

Through the treatment process described above, a second thermoelectric structure is formed with the second thermoelectric bodies 17 formed on the substrate 10.

Subsequently, as shown in Fig. 41, a pair of the first thermoelectric structure 41 and the second thermoelectric structure 42 are bonded together with an epoxy-based adhesive 43 such that the surfaces of the respective structures on which the photosensitive resin 12a and 12b are formed face each other.

The above-mentioned bonding is carried out such that the unopened surface areas of the photosensitive resin 12a formed on the surface of the first thermoelectric assembly 41 fit into the upper surface of the second thermoelectric bodies 14.

Through the connection, as shown in Fig. 41, the unopened surface areas of the photosensitive resin 12b formed on the surface of the second thermoelectric surface structure 42 into the upper surfaces of the first thermoelectric bodies 15. Thus, a structure is formed in which the relative position of the first thermoelectric bodies 15 and the second thermoelectric bodies 17 remains within a fixed distance, which facilitates an operation of wiring among the thermoelectric bodies to be attached at a later stage.

As can be seen from Fig. 41, the first thermoelectric bodies 15 and the second thermoelectric bodies 17 are mutually out of contact with each other and electrically insulated from each other until wiring is provided at a later stage of processing.

After bonding the first thermoelectric assembly 41 to the second thermoelectric assembly 42 as described above, the polymer film 19 is separated and removed from the bottom surface of the substrate 10 using toloin. Then, the first thermoelectric assembly 41 and the second thermoelectric assembly 42 in a combined state are subjected to heat treatment in a nitrogen atmosphere at a temperature of 350°C for one hour.

The heat treatment in a nitrogen atmosphere is used to homogenize the chemical composition of the alloys constituting the first thermoelectric bodies 15 and the second thermoelectric bodies 17, which contributes to increasing the output of a thermoelectric power generating element.

Although the heat treatment is applied in a nitrogen atmosphere at a high temperature, the amount of deformation such as thermal contraction occurring to the photosensitive resins 12a and 12b after patterning is minimal, thereby causing no practical problems, provided that an exposure treatment is applied to the photosensitive resin. che resin 12 with light-sufficient intensity when a patterning treatment is applied to the photosensitive resin 12 as shown in Fig. 37.

The thermoelectric power generation element having the first thermoelectric structure 41 combined with the second thermoelectric structure 42 is cut into a desired length.

When the surface roughness of the cut end surface of the above-mentioned member is so large or cracks occur at the bonded interfaces due to insufficient use of the adhesive 43 that the wiring is affected at a later stage of processing, the cut end surfaces may be polished by a lapping process or the like.

In particular, when cracks occur at the bonded interfaces due to insufficient use of the adhesive 43, the cut end surfaces may be polished by a lapping process after filling the cracks at the bonded interfaces with an insulating resin such as an epoxy resin.

Subsequently, all the copper forming the substrate 10 is dissolved by immersing the entire element in a nitric acid solution and then the titanium forming the electrode film 11 is dissolved and removed by using a hydrogen fluoride solution.

A gold (Au) film is formed on the entire surface at each of the cut ends of the element by a vacuum deposition process, a sputtering process or an electroless plating process. Then, as shown in Fig. 42, wiring electrodes 45 are formed by patterning the gold film by the photolithographic techniques, thereby forming a synthetic thermoelectric structure 44.

Each of the first thermoelectric bodies 15 is connected through corresponding wiring electrodes 45 to one of the second thermoelectric bodies 17 formed opposite to the former on the surface at the cut end, thereby forming a thermocouple 50.

As described in the foregoing, all the thermoelectric bodies provided at predetermined intervals within each of the synthetic thermoelectric structures 44 can be connected as a whole without faulty wiring by the wiring electrodes 45.

As shown in Fig. 43, a plurality of the synthetic thermoelectric assemblies 44 are stacked in alternate layers such that each of the first thermoelectric bodies 15 of one of the synthetic thermoelectric assemblies 44 is opposed to each of the second thermoelectric bodies 17 of another synthetic thermoelectric assemblies 44 via a flat sheet-shaped insulator 41 made of acrylic resin, see Fig. 41, and they are bonded by an epoxy-based adhesive.

The insulator 41 is used to prevent the first thermoelectric bodies 15 from coming into electrical contact with the second thermoelectric bodies 17 (see Fig. 41), and also to increase the mechanical strength of the thermoelectric power generation unit as a whole. The insulator 51 is formed to have a thickness of 50 µm.

In the next step, as shown in Fig. 45, element terminal wirings 52 are formed along respective edges of the surface at both cut ends of each of the synthetic thermoelectric structures 44 using a conductive adhesive. The wire formed in this process can be used for element connection wiring.

All the thermocouples 50 are connected together in series by connecting the edges of the respective first thermoelectric bodies 15 to those of the respective second thermoelectric bodies 17, both of the bodies being incorporated in the respective synthetic thermoelectric structures 44, with the corresponding element lead wire 52, thereby forming a thermoelectric power generation unit.

The above-described element connection wirings 52 can be provided with ease because the element connection wirings 52 do not require as great an accuracy as that required in the case of forming the wiring electrodes 45 of the wiring of the thermoelectric bodies in the aforementioned processing step.

In the manufacturing process of a thermoelectric power generation unit, patterning with an accuracy of plus or minus several µm may be provided on the dry film constituting the photosensitive resin 12 formed by photolithographic techniques.

Also, the first thermoelectric bodies 15 and the second thermoelectric bodies 17 can be formed with an accuracy of plus or minus several µm along the surface of the photosensitive resin 12a and 12b, respectively.

Such accuracy as described above represents a remarkably high accuracy compared to that in the case of the thick film method in which the coating is applied by a conventional machining process or the printing process. Furthermore, the thickness and chemical composition of the thermoelectric bodies formed by the plating process can be controlled with ease. and pre-processing of only the materials of the solution process is easier than in the conventional processes.

The manufacturing processes of a thermoelectric power generation unit as described in the foregoing include a photolithographic process, a plating process, a film forming process and an etching process, all of which can be applied on a batch basis. Therefore, they have an advantage of being able to manufacture a plurality of the elements simultaneously.

As stated in the foregoing, the thermoelectric power generation unit manufactured by the above-described methods comprises the thermoelectric bodies each of which has a width of 150 µm, is provided at a pitch of 50 µm, and has a total thickness of 150 µm including the insulator 150.

Assuming that the width of the substrate 10 is 1 cm and the thickness of the entire body of the layered structure is 7.5 cm, the number of thermocouples that can be formed on the substrate 10 is 2500 elements.

When a temperature difference of 2ºC is applied to the thermoelectric element, an open circuit voltage of approximately 2 V is output, which is a sufficient output voltage to drive electronic equipment such as a wrist watch.

Assuming that a length of the thermoelectric power generating element is 2 mm, the internal impedance becomes about 13 kΩ, which shows that this is of a magnitude that electronic equipment can easily cope with.

In this embodiment, a copper sheet is used as the material for the substrate 10, other materials that are not attacked by the thermoelectric process materials, dry film or polyimide, but which are soluble by the etching process, can be substituted for the copper.

The use of metal materials such as a steel sheet, a nickel sheet, a galvanized iron sheet, an aluminum sheet, a titanium sheet, a brass sheet or the like is contemplated for use in the substrate 10. Also, materials such as a glass plate, an alumina sheet or the like may be used as the material for the substrate 10.

Other metal films other than a titanium film, if they are made of materials insoluble in a plating solution, may be substituted for the electrode film 11 made of a titanium film and formed on the substrate 10. A gold (Au) film, a platinum (Pt) film, a palladium (Pd) film, a tantalum (Ta) film, or the like are prospective other materials.

Not only an Au film but also other metal films can be used to form the wiring electrodes 45.

Regarding the material of the wiring electrode 45, a copper (Cu) film, a nickel (Ni) film, or an iron (Fe) film, etc. are applicable to the wiring electrode 45.

For forming the wiring electrodes 45, a printing process or a process of sticking the electrodes patterned on the surface of another material in a sheet form may be applicable.

Further, to form the element connection wirings 52, a process of forming a metal film by vacuum deposition, sputtering, printing or a process of sticking the electro those patterned on the surface of another material in sheet form.

In the embodiments of the invention, the photosensitive dry film is used as frame members when plating is carried out with the thermoelectric materials. Besides the dry film, a photosensitive polyimide can also be used for the same purpose. In addition, when the necessary thickness of metal deposition by plating is on the order of only 10 µm, a rubber-based photoresist or a cinnamic acid-based photoresist can be used.

Besides the acrylic resin described above, a material that is electrically insulating, low in thermal conductivity, and can easily withstand a temperature difference occurring at the thermoelectric elements can be used to form the insulator 51. An epoxy resin can be used for the insulator 51.

Although in this embodiment, the thickness of the thermoelectric bodies is set to half that of the photosensitive resin, the thickness of respective thermoelectric bodies may be selectable within the range in which the thickness of the thermoelectric bodies is less than that of the photosensitive resin, provided that the first thermoelectric structures 41 and the second thermoelectric structures 42 fit well with each other.

INDUSTRIAL APPLICABILITY

By the manufacturing method of a thermoelectric power generation unit according to the invention, a micro-sized thermoelectric power generation unit capable of generating a sufficient output voltage can be manufactured with ease and high accuracy.

As a result, the thermoelectric power generation unit can be extensively used as a power supply source for a micro-sized portable electronic equipment, for example, a wristwatch.

Claims (7)

1. Manufacturing method of a thermoelectric power generation unit comprising: a first formation process of a thermoelectric structure with the steps: Forming an electrode film (11) made of a metallic material on a substrate (10), Providing a pattern of a photosensitive resin (12) in the form of stripes on the electrode films (11), Forming a plurality of first thermoelectric bodies (15) in a regular arrangement by plating a first thermoelectric material within openings (13) provided in the photosensitive resin (12) using the electrode film (11), Coating the photosensitive resin (12) and the first thermoelectric body (15) with a thermosetting resin (16) and Dissolving and removing the substrate (10) and the electrode film (11); a second formation process of a thermoelectric structure with the following steps: forming an electrode film (11) made of a metallic material on a substrate (10) other than the above-mentioned substrate, Providing a pattern of a photosensitive resin (12) in the form of stripes on the electrode film (11), Forming a plurality of second thermoelectric bodies (17) by plating a second thermoelectric material within openings (13) provided in the photosensitive resin (12) using the electrode film (11), Coating the photosensitive resin (12) and the second thermoelectric body (17) with a heat-curing resin (16) and Dissolving and removing the substrate (10) and the electrode film (11); and Forming a plurality of thermocouples (30) in series as a thermoelectric power generating element by a process comprising the steps of: Connecting a plurality of the first thermoelectric structures (20) and the second thermoelectric structures (21) to each other laid in alternating layers, and alternately connecting the adjacent end surface of each strip of the first thermoelectric bodies (15) and the second thermoelectric bodies (17) to wiring electrodes (25). 2. Method according to claim 1, in which, instead of the thermosetting resin (16), a heat-insulating sheet (18) is bonded to the photosensitive resin (12) and the thermoelectric bodies (15, 17). 3. Method according to claim 2, in which the surface of the first thermoelectric bodies (15) is bonded to the surface of the second thermoelectric bodies (17) with a heat insulating sheet (18) provided therebetween before the substrates (10) and the electrode films (11) are dissolved and removed, and then dissolving and removing both substrates (10) and the corresponding electrode films (11). 4. Method according to one of claims 1 to 3, in which the substrates (10) and the electrode films (11) are replaced by electrically conductive substrates (10). 5. Method according to one of claims 1 to 3, in which the surface or the entire body of the substrate (10) has insulating properties, in which metal films are formed on the substrate (10) instead of the electrodes (11), in which the respective metal films are etched into a first electrode film (31) and a second electrode film (32) which are formed in the shape of two combs facing each other, each tooth being alternately interposed between adjacent teeth, and wherein the pattern is formed in the form of stripes in the gap region between the first electrode film (31) and the second electrode film (32), each in the form of teeth of a comb. 6. The method according to claim 5, wherein another metal film is formed on an entire plating initiation surface (33) exposed by dissolving and removing the substrate (10), the first electrode films (31) and the second electrode films (32), and the other metal film is patterned in wiring electrodes (35) by etching. 7. Method according to claim 3, in which the heat-insulating sheet (18) is replaced by an insulator (51), wherein the thickness of the thermoelectric bodies (15, 17) is formed smaller than that of the photosensitive resin (12a), and wherein in the second thermoelectric assembly forming process, the photosensitive resin (12b) is formed with a second pattern formed at the same pitch as that of the first pattern, and unopened surface areas each narrower than the width of each of the openings in the first pattern and openings (13b) each wider than the width of each of the unopened surface areas in the first pattern are provided.